The cabin of an aircraft flying relatively high altitudes must be sealed and supplied with pressurized ventilation air for the comfort of the passengers. The ventilation system of an aircraft thus typically includes one or more ducts through which pressurized and temperature conditioned supply air is conveyed into the cabin. Overhead nozzles, adjustable both in directional orientation and rate of airflow are provided in some such systems to give each passenger limited control over the ventilation and velocity of supply airflow in their immediate environs. Unfortunately, relatively high noise levels and drafty conditions objectionable to adjacent passengers often result when these nozzles are fully opened and oriented without regard to the comfort of adjacent passengers.
More recently, such individually adjustable nozzles have been eliminated from aircraft ventilation systems in favor of more diffuse ventilation airflow introduced through a diffuser duct centered along the cabin ceiling. A plurality of orifices in fluid communication with the interior of the duct convey pressurized supply air downwardly into the cabin space to provide ventilation. One drawback to the prior art diffused ventilation systems is that they do not permit smoke and other contaminants to be efficiently cleared from the cabin.
In attempting to achieve better smoke and contaminant control, a ventilation system has been developed for supplying pressurized air through discharge slots or orifices formed in a supply duct running along the length of the cabin, and disposed where the bin's upper surface meets the downwardly curved ceiling. A plurality of slots comprising the duct output nozzle are disposed immediately adjacent the top surface of the storage bin. For proper distribution, the velocity of air flowing through the slots must be sufficient to "attach" the flow to the upper surface of the storage bin so that it follows that surface down into the cabin, a physical phenomenon known as the "Coanda Effect". Ventilation air flowing down into the seating area along the top surface of the storage bin on each side of the cabin tends to distribute symmetrically about a line (or vertical plane) that extends along the longitudinal axis of the cabin.
If the flow of air from the supply duct is below the critical velocity necessary to attach the airflow to the upper surface of the storage bin, it has been observed that the air may instead flow along the ceiling toward the opposite side of the cabin, mixing with the flow from the supply duct at the other side, thereby producing a very asymmetric airflow distribution throughout the cabin. Poor airflow distribution symmetry has been generally an accepted drawback of prior art ventilation systems, because concerns related to efficiently clearing passenger-generated carbon dioxide and cigarette smoke from the cabin were not emphasized to the extent they now are.
Since symmetrical distribution of ventilation airflow can be achieved by increasing the velocity of the supply air through the nozzle, it would appear that his problem could be easily solved. However, it has been found that providing supply air through the discharge slots at sufficient velocity so that the airflow attaches to the upper surface of the storage bin, produces a symmetrical airflow distribution having an unacceptable velocity in the passenger seating area, i.e., the average passenger tends to complain that the cabin is "drafty" and thus uncomfortable. In this instance, the obvious solution fails to resolve the problem.